A synthetic fuel is a manmade material synthesized by the union of chemical elements, groups, or simpler compounds or by the degradation of a complex compound and is used to produce heat or power by burning. The majority of synthetic fuels are generated by the degradation of complex materials such as coal, oil shale, oil sand or natural gas. Synthetic fuel generation by the degradation of complex organic materials typically requires energy in the form of heat, as well as pressurized processing conditions, special chemical catalysts and highly reactive chemical reagents. Synthetic fuels produced through degradation of complex materials are often toxic flammable liquids or gases that require special storage and handling. Typical examples of synthetic fuels are synthetic oil produced from coal, synthetic gas (syngas) produced from coal, synthetic diesel fuel derived from natural gas, synthetic gasoline derived from natural gas, synthetic oil derived from oil shale and synthetic oil derived from oil sand.
A second means of producing a synthetic fuel is to react a complex organic material with a second reagent to yield a new material without degradation. Reactions of coal with numerous simple organic chemicals are well documented and are often used to study the various reactive chemical functional groups present in coal. Examples of reactions of coal with organic chemicals include acetylation with acetic anhydride and alkylation with benzyl bromide. Such reactions can impart beneficial properties to a fuel product and allow the production of coal derived solid synthetic fuels with lower toxicity and easier handling than traditional synthetic fuels. Although many reactions of organic reagents with coal are known, the products of such reactions do not demonstrate sufficiently advantageous fuel properties to justify the high cost of large-scale synthetic fuel production.
Coal-based synthetic fuels can conceivably be used in any application where coal is used, however, most coal-derived synthetic fuels are used in one of two industries, electric power generation and coke production. In electric power generation, coal-based synthetic fuels are typically burned alone or with coal in power generation facilities. In coke production, the synthetic fuel can be used alone or with metallurgical coal. In this case the coal used to produce synthetic fuel must be metallurgical grade coal.
Asphalt emulsions, oil emulsions and carboxylated styrene butadiene copolymers have been used as additives to generate synthetic fuels. Synthetic fuels made from these suffer from disadvantages in that their lower reactivity results in higher dosage requirements and the attendant cost. These materials also typically add significant moisture to the coal, giving the resulting material lower BTU value. In certain crushing and grinding operations where a particular particle size is desired, the particles have been shown to re-agglomerate due to the presence of the additive. Handling problems may result from the presence of the additive. These products may also have attendant environmental and health concerns due to the presence of volatile organic compounds. Some of the additives require acid treatment of the coal which raises health and liability concerns at synthetic fuel production sites. Potentially hazardous conditions arise due to the high temperatures needed to feed and maintain some synthetic fuel additives. Incompatibility of the synthetic fuel additives with synthetic fuel plant equipment such as conveyor belts has been observed at some sites.
An object of the invention is to provide a method of preparing a synthetic fuel from coal that has advantages over existing technology in the areas of handling, synthetic fuel milling and pulverizing, additive toxicity and environmental acceptability.